I'm wondering what the header mentioned above is. It's included in the response when I do JSONP calls to Facebook, or even when I simply access http://static.ak.fbcdn.net/
I haven't found any documentation on facebook, e.g. on https://developers.facebook.com/docs/reference/ads-api/etags-reference/
So, hope somebody can help me. thx!
To me, this seems to be a request tracking id, so that Facebook can find and trace an specific request details [faster] when you fill in a bug report. Have seen them in lots of bug reports on their bug tracker.
A little late, but just to add more information that I think it's useful. Facebook has now a place for it in its documentation, we can find it here
If you need to report a bug in the Graph API, we include a couple of additional request headers that you should send with your bug report to help us pinpoint and reproduce your issue. These request headers are X-FB-Debug and x-fb-rev.
来源：https://stackoverflow.com/questions/15612794/what-is-the-x-fb-debug-header-returned-from-facebook